1. Field of the Invention
The present invention relates to an automatic transmission for a vehicle. More particularly, the present invention relates to a planetary gear train of an automatic transmission for a vehicle that improves power delivery performance and fuel economy by achieving nine forward speeds using minimized constituent elements.
2. Description of Related Art
In recent years, a rise in oil price causes dashing into unlimited competition for enhancing fuel efficiency.
As a result, research into reduction of weight and the enhancement of the fuel efficiency through down-sizing are conducted in the case of an engine and research for simultaneously securing operability and fuel efficiency competitiveness through multi-speeds are conducted in the case of an automatic transmission.
However, in the automatic transmission, as the number of speeds increase, the number of internal components increase, and as a result, mountability, transmission efficiency, and the like may still deteriorate and cost and weight may increase.
Accordingly, development of a planetary gear train which may bring about maximum efficiency with a small number of components may be important in order to increase a fuel efficiency enhancement effect through the multi-stages.
In this aspect, in recent years, 8 and 9-speed automatic transmissions tend to be implemented and the research and development of a planetary gear train capable of implementing more transmission steps has also been actively conducted.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.